348
FXUS63 KDTX 051812
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
112 PM EST Wed Feb 5 2025

.KEY MESSAGES...

- A Winter Weather Advisory is in effect for locations along and
  south of I-69 this evening through Thursday morning.

- A brief period of snow occurs ahead of a rapid transition to longer-
  duration freezing rain for Metro Detroit while snow/sleet are more
  dominant north of I-96.

- Ice accumulations up to a tenth of an inch will be possible in the advisory.
  Up to an inch of snow/sleet accumulation will be possible across
  all of SE Michigan.

- Colder air returns Thursday night with gusty westerly winds, in
  excess of 30 mph at times.

- Another mixed precipitation event is possible this weekend with
  potential for accumulating snowfall and additional icing.

&&

.AVIATION...

Incoming episode of winter weather is still timing out as prior
forecasts indicated. Expecting a concoction of light snow and sleet
to overspread the airspace just prior to midnight. Light freezing
rain will mix and become the dominant type at the Detroit area
terminals by 07z (2am EST). Only a few hours of meaningful icing
rates (up to 0.03"/hr) are expected prior to 12z (7am EST) before
quickly shutting off. At FNT and MBS, the precipitation will be
lighter and of shorter duration - though some degree of mixing is
expected at both - with more freezing rain potential at FNT.

Ceilings will progressively lower this evening into MVFR and pop
down to IFR with the peak of the precipitation and will linger for a
few hours before slowly lifting during the morning. Otherwise, light
easterly winds today and tonight will flip to westerly after sunrise
Thursday and gain a gust component before noon.

For DTW...a narrow plume of moisture and MVFR clouds may squeeze in
off of Lake Erie after 22z. There may be a brief period of flurries
or very light freezing drizzle with this feature - but chances are
low (< 15%). The main winter event window will be 05z-11z with a
light snow/sleet mix transitioning to light sleet/freezing rain
ultimately to light freezing rain. The westerly winds will gust over
30kts by mid/late Thursday afternoon as clouds scatter out behind
the system.

DTW THRESHOLD PROBABILITIES...

* High in ceiling at or below 5000 feet tonight into Thursday
  afternoon.

* Medium confidence in the timing of precipitation type changes
  tonight between 05z-11z; start as light snow/sleet, then
  light sleet/freezing rain, then finally light freezing rain.

&&

.PREV DISCUSSION...
Issued at 420 AM EST Wed Feb 5 2025

DISCUSSION...

Sprawling high pressure will track across the area through this
afternoon, ensuring a dry forecast for most of the daytime hours.
NBM solution remains an outlier in producing measurable QPF/snow
this afternoon/evening, likely latching onto the deformation and FGEN
that will be lifting into lower Michigan at that time. Will take a
lot to overcome the 20+ degree dewpoint depressions that forecast
soundings depict at this time though, but cannot rule out a few
flurries.

The main focus of this forecast period however is upstream where
substantial moisture transport will be occurring into the Plains
region. This moisture interacts with a rather low amplitude
shortwave to direct the next weather system into SE Michigan this
evening through Thursday morning. As advertised for the past several
days, mixed precipitation is expected during this event with light
snow and ice accumulations anticipated especially over the southern
tier of SE Michigan counties. A Winter Weather Advisory was issued
with this forecast package given the timing of the wintry mix just
prior to the morning commute.

Starting with the higher certainty items: model data is quite
consistent in bringing the shortwave to lower Michigan after 10 PM
EST, which will introduce a fleeting but sufficient deep layer of
moisture to produce QPF on the order of 0.1 to 0.15" by Thursday
morning. Peak precipitation rates are expected between 05z to 10z
(Midnight to 5 AM EST) amidst the deepest/strongest ascent (omega of
20-25 ubar/s). The highest uncertainty item is still the phase in
which this precipitation falls to the ground (snow vs sleet vs
freezing rain) and how long each of these phases lasts. There is
increasing confidence that precipitation will begin as all snow, as
the aforementioned shortwave brings a fleeting but sufficient
moisture depth into the DGZ. Forecast soundings continue to trend
colder, such that as long as ice nuclei is present favored p-type
remains either snow or sleet even as the warm nose arrives. This is
evident as the warm layer is quite shallow (around 2.0 kft deep and
Tmax of 1 C) compared to the deep cold layer (4.0 kft deep and Tmin
of nearly -7 C). These conditions will be favorable for refreezing of
likely only partially melted ice crystals, if they melt at all.
Snow/sleet accumulations will be subject to very low snow-liquid
ratios (5-7:1) and a large degree of riming, so accumulations should
hold under one inch during this phase of the event.

The transition to freezing rain is expected after the shortwave
departs and strips away ice nuclei from the column, which per model
soundings looks to occur between 07-09z (2am-4am). Overlap with the
higher rates will be minimal, but in general we still look to grind
out around about 0.01-0.02" per hour of liquid through the mid
morning hours which will be enough to produce a light coating of ice
up to a tenth of an inch. Near the Ohio border where there is a bit
more of the warm nose influence and earlier changeover potential,
localized ice accumulations up to 0.15" will be possible. The column
will gradually lose moisture depth to taper off freezing rain to more
of a freezing drizzle before temperatures rise above the 32 degree
mark by late Thursday morning. Daytime highs peak in the mid to upper
30s but drop back into the teens Thursday night as a cold front
drops through the region. This front will be associated with a deep
upper level trough carrying an impressive low level jet presence of
50-60 knots in the lowest 5.0 kft agl. Gusty westerly winds of 30 to
40 mph thus are likely Thursday evening through Friday morning.
Frequent gusts are expected to hold below advisory thresholds per
current data.

The end of the work week will be drier but cooler with temperatures
dropping a few degrees below normal (daytime highs in the mid 20s to
low 30s). The colder airmass may activate Lake Michigan
stratocumulus, but a very dry column aloft keeps conditions dry.

Finally, attention turns to potential for a strong low pressure
system to impact the Ohio Valley/Great Lakes this weekend.
Deterministic and ensemble guidance both suggest accumulating snow
will be in play with this system as well as mixed precipitation,
which is progged to have a much larger degree of synoptic support
than the system we will see tonight. There are still plenty of
scenarios that could play out regarding the track of the system
which will substantially impact precipitation amounts and
precipitation type. This will be one to monitor heading into the
weekend.

MARINE...

High pressure builds into the Great Lakes this morning, maintaining
light winds and waves through the day. A low pressure system then
tracks through the region overnight tonight through Thursday
morning, bringing light snow and a wintry mix. Strong westerly winds
are forecast to develop Thursday afternoon and evening as the
departing system ushers in an arctic air mass. A Gale Watch remains
in effect for Lake Huron Thursday afternoon through Friday morning
with peak gusts likely to reach 40 knots over parts of the lake
Thursday evening. Snow showers/squalls and freezing spray will
likely accompany the arctic air Thursday night into Friday. An area
of high pressure then briefly slides across the region early
Saturday before the next low pressure arrives Saturday night,
bringing strengthening northeast winds and another round of wintry
precip.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from midnight tonight to 9 AM EST Thursday
     for MIZ060>063-068>070.

     Winter Weather Advisory from 10 PM this evening to 9 AM EST
     Thursday for MIZ075-076-082-083.

Lake Huron...Gale Watch from Thursday afternoon through Friday morning for
     LHZ361>363-421-422-441>443-462>464.

Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

AVIATION.....Mann
DISCUSSION...MV
MARINE.......TF


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